Modern television monitors require a high quality picture with clear sound, transparent treble and deep powerful bass.
To achieve deep low frequency bass, a subwoofer system is required inside the television set enclosure. In view of the fact that enclosure space is limited in modern sets, the bass produced sounds weak and the performance is unsatisfactory.
Passive radiator loudspeaker systems are an improvement over the conventional bass reflex system. The systems do not produce turbulent sound at the port of the bass reflex system and radiate reflected sound from inside the enclosure. This colors the sound quality. Furthermore, port length can present a problem in small enclosures. The frequency response of the system can be easily tuned with the appropriate speaker diaphragm size, weight and compliance of the passive radiator. As for loudspeaker diaphragm and bass reflex tube cross-sectional size, the greater the size of passive radiator, the higher the sound pressure level (SPL).
The advantage of a passive radiator system over a bass reflex system in television enclosures was discussed in U.S. Pat. Nos. 5,892,184 and 6,658,129. D'Hoogh's passive radiator is not contoured and as a result it does not provide an optimum bass sound pressure level.
One of the important loudspeaker specifications is polar directivity. At high frequencies, the sound is very directional toward the front and strong on axis. At mid frequencies, the sound is less directional and spreads sideways. The lower the frequency, the wider the spreading, while the front intensity is the strongest. The sound one hears from a loudspeaker is influenced by the placement of the loudspeaker. Generally, the listening room has more parallel walls that produce a phenomenon known as standing waves. The existence of standing wave patterns produces irregularity in the sound pressure level in various places within the room. This effect can be easily heard from the bass sound. This irregularity can be minimized by using various acoustic devices such as combination of absorbers, diffusers, bass traps, etc. Although useful, these devices increase the cost of the unit.
The present invention overcomes the drawbacks of the prior art with a contoured passive radiator design. The contour of the radiator follows the contour of the television enclosure where the radiator is mounted. As a result, the passive radiator size can be maximized. For example, a contoured passive radiator equivalent to 8″ diameter or larger can be mounted on a small 14″ television set. For large televisions, for example 29″, a contoured passive radiator equivalent to a 10″ diameter or larger may be used.
By making use of a contoured passive radiator, the above disadvantages can be alleviated. The contoured passive radiator is less directional compared to a conventional diaphragm. The sound spreads in a wider direction, hence reducing the irregularity of the SPL of the bass sound. The invention is applicable for use in audio components, high fidelity loudspeakers, subwoofers and other loudspeaker systems.